The primary scheduling requirement for the Spitzer Space Telescope has been to maximize observing efficiency while
assuring spacecraft health and safety and meeting all observer- and project-imposed constraints. Scheduling drivers
include adhering to the given Deep Space Network (DSN) allocations for all spacecraft communications, managing data
volumes so the on-board data storage capacity is not exceeded, scheduling faint and bright objects so latent images do
not damage observations, meeting sometimes difficult observational constraints, and maintaining the appropriate
operational balance among the three instruments. The remaining flexibility is limited largely to the selection of
unconstrained observations and optimizing slews. In a few cases, the project has succeeded in negotiating DSN tracks to
accommodate very long observations of transiting planets (up to 52 hours to date with even longer requests anticipated).
Observational efficiency has been excellent with approximately 7000 hours of executed science observations per year.